DESCRIPTION Abstract: There are currently 14 million U.S Veterans over the age of 55 according to the 2010 U.S. Census. Research has indicated that motor declines begin to accelerate within this age group and beyond as does incidence of motor pathology. Aerobic exercise is currently under investigation for its potential in increasing cortical plasticity and offering improved outcome for rehabilitation of motor disorders. Exciting new studies (* denotes VA sponsored research) present the possibility that aerobic exercise may lead to significant improvements in upper extremity function (McGregor et al., 2009*; McGregor et al., 2011*; Voelcker-Rehage et al., 2010; Ploughman et al., 2008) in both aging and disease. However, the mechanisms by which fitness exerts its benefits have yet to be fully understood. New research has shown that upper extremity performance is associated with aging-related losses in interhemispheric inhibition (Bernard & Seidler, 2011; Fling & Seidler, in press; McGregor et al., 2009), which begins even in middle age. Our lab has recently shown that these changes may not be inevitable or immutable. New evidence indicates increased levels of physical fitness through aerobic activity may mitigate losses in interhemispheric inhibition and improve motor performance. This research proposes to enroll sedentary older Veterans into a program consisting of upper extremity behavioral training and regular engagement in physical activity. We hypothesize that motor performance will be linked to levels of interhemispheric inhibition (assessed by advanced neuroimaging) and both will improve over the course of our exercise intervention. We believe this research is critical to our understanding of normal motor organization and how it changes due to aging processes will inform our capability for reclamation of motor capacity due to neural pathology, as cortical activation patterns may vary according to biological age. The goal is that this work will eventually be applied to rehabilitation of motor deficits, which occur with increase incidence within and beyond middle age.